- These are complexes which contain carbonyl
ligands, bonded to a metal with a negative
e.g Re(CO)- 5
, Mn(CO)- 5
- Preparation: When sodium amalgam is taken in
dry tetrahydrofuran and treated with Fe(CO)5 ,
Na2[Fe(CO)4] is obtained. (Iron is in -2 state)
- When sodium amalgam is treated with
Re2(CO)10 , Na[Re(CO)5] is obtained. (Re is in -1
- Carbonylates are used in organic synthesis. Aldehydes
(containing α-H atom) or ketones on treatment with
fomaldehyde and KHFe(CO)4 undergo reductive methylation.
- α,β unsaturated carbonyl compounds on treatment with
K[Fe(CO)4] yield their saturated derivatives.
- KFe(CO)4 / KHFe(CO)4 on treatment with α,β unsaturated esters
yield corresponding malonates. (Note: KFe(CO)4 is called
A B C
- In the above reactions, product B is obtained
when one mole of each reactant is used. If two
moles of the reagents are used, then product C
- Cyanuric fluoride on reaction with KMn(CO)5 at
low temperature yields substituted compounds.
• Bonding in carbonylates is similar to that in
• The metal will be in a negative oxidation state.
• The orbitals of the oxygen lie at a lower level
than the corresponding orbitals of the carbon,
due to the greater electronegativity of oxygen.
• (Note: Draw MO diagram of CO as given in
• 18 electron rule is valid in most cases.